Thermally insulated glass window constructions conventionally employ various forms of an extruded frame of a single piece (for example, such as shown in U.S. Pat. No. 4,006,569 to KAIN) or of two pieces thermally insulated from each other (for example, such as shown in U.S. Pat. No. 3,992,843 to DiFazio) into which is inserted a glass panel known as "double-insulated glass" or DIG, comprising two or more parallel panes of glass thermally insulated from each other by a sealing spacer located at or adjacent the free edge of the panes. The extruded frame constructions, many forms of which are in the public domain, typically are made of plastic, such as PVC or the like, and generally take the form of a rigid, U-shaped channel member provided with flexible ribs on the upper interior facing portions of the arms of the channel member for sealingly retaining the DIG panel and the channel member together.
In the fabrication of thermally insulated glass panel constructions in which the composite glass-spacer-glass edge surface of the DIG panel is coated with a sealant or the sealant is applied to just the edge of the spacer, the extruded frame is first positioned so that the edge surface of the DIG panel faces the base of the channel of the channel member to be installed, and then the channel member is pushed over the DIG panel edge, past the flexible ribs, to or near the bottom of the channel.
The prior constructions made in this manner are structurally sound and thermally efficient, but have proven to be aesthetically unacceptable. The sealants used, most commonly polysulfide, butyl rubber or polyurethane, are black in color, and no matter how carefully applied, there is inevitably some smearing or smudging of the sealant with the result that specks or small pieces or smears (hereinafter collectively "smudges") of the unsightly black solidified sealant find their way to the outside surfaces of the DIG panel adjacent the edge. Even when manufacturers go to the costly extra step of hand-cleaning the glass surfaces adjacent the edges to remove as much of such smudges as possible, the problem remains.
With such smudges on the outer glass surfaces adjacent the DIG panel edge, as the channel member is pushed over the DIG panel edge, these smudges of hardened black sealant are picked up by the interior of the channel member, especially the flexible ribs, and these smudges move along and between the channel member arms and the glass pane surfaces of the inserted DIG panel opposing the channel arms. While cleaning may be effected after such assembly of those portions of the glass surfaces which lie outside of the channel member, such cleaning cannot be extended to those portions of the DIG panel near the edges which portions are covered by the channel members, inasmuch as they are inaccessible from outside the channel members. Thus, when the DIG panel is viewed from one side, through the panes, to the other side, the black sealant smudges on the inserted surfaces of the DIG panel remain visible and are found by customers to be extremely unsightly.
One solution which has been used to solve this problem is to limit penetration of the DIG panel within the channel member to a depth only where the spacer between the panes is completely inserted. While this solution is cosmetically acceptable, the resulting window frame construction is structurally and thermally weak and unsound.